A couple of distinctive features in Robert Frost’s poem “Mending Wall” give us a clue about its tone. One of these features is Frost’s twisted but rich syntax, as we can see in the poem’s opening lines:
Something there is that doesn't love a wall,
That sends the frozen-ground-swell under it
The other unusual aspect of the poem is that it frequently poses riddles and questions but leaves them unanswered. The poet puzzles over the boulders of his boundary wall toppling over repeatedly, almost of their own volition. But exactly, what is the “something” that won’t allow the stones to stay put? Frost doesn’t tell us.
Because of the idiosyncratic, roundabout syntax, and the questions raised in the poem, its tone is inquisitive, though tempered with humor, mischief, and gentleness. More than the poet, his neighbor is bothered by the shifty wall between their estates, often spouting the platitude:
Good fences make good neighbors
The poet questions this cliche, but he does not judge his neighbor too harshly for partaking in it. Mischievously, he wonders if he should put the idea in the neighbor’s head that it is the “elves” who are taking down the wall. Yet, he does not do so, wanting the neighbor to come up with such subversive notions himself. Thus, though the poet disagrees with the neighbor, he does not wish to control his thoughts. His tone is one of quiet acceptance.
Further, although the poet can see that the neighbor is like an “old stone-savage armed,” or set in his limited way of thinking, he acknowledges that the neighbor is pleased with his own thought process:
And he likes having thought of it so well
He says again, ‘Good fences make good neighbors.’
Therefore, at a deeper level, the poem’s mood is one of co-existence. To fight with a narrow-minded neighbor would be propagating another cliche, which the poet is loathe to do. His tone towards the wall—which, it should be noted, he keeps mending alongside the neighbor every spring—is of playful forbearance.
Finally, walls such as the one in the poem, do exist in the world, like arbitrary political boundaries. Though the poet questions their purpose, he plays along with their illusion, hoping one day his neighbor too will see they don't need a boundary wall to keep the apple trees of one eating the pine cones of the other! Thus, the poem's tone is also that of allegory, where the wall could stand for a border between countries. Are such borders necessary, or do they create an atmosphere of alienation and suspicion? The poet leaves us with an important question.